i see these sensors that are 195 on and 175 off. now if that was on my car it would never turn off because it will reach 195 no problem after sitting at lights but once moving my car on average temperature days will never go lower then 180 . am i on the right track and thats what would happen or do i have it all wrong? even a 195 on and 185 off would not suit me as 185 is probably about the most consistent temp my car runs at so it would be on and off more than a light switch. what do you all do to combat this? i dont particularly want it hitting any higher than 195.

 

You already have the electric fans in and running?

 

in my 81 vet i do which has a manual switch to control my fan . this is for my other car and was considering an automatic switch for it but have always wondered how this aspect of that style of sensor would work when the cooling system doesnt have the potential to drop to 175 no matter how long the fan is on.

 

Once the temp reached 195 the fan would kick in and never cut off, unless the temp dropped below 175, there just dumb hysteresis switches.

 

Not very familiar with these auto sensors but there has to be a difference in temp going in the radiator verses coming out.If the auto sensor is on the cooler coolant coming out of the rad and the dash gauge sensor is on the hot coolant coming out of the engine this might be the difference.If that makes sense.

 

What temp thermostat do you have in the car? If it is 180F [or higher], you can run the fans continuously and it will never go below the stat temp....the stat will just close enough to keep the temp up. Now, your cooling system may not allow the coolant temp to go below 180F either; but you'll never know that unless you take the stat out or put a 160F stat in to find out.

 

If you look at Jegs or Summit Racing catalogs they sell fan temperature sensors according to the thermostat you are running; 160, 180, 195, etc.

 

Sitting at a light or in traffic the fan will come on and then it will stay on pulling the temp down to 175 degs. ( if your fans are good enough ) then it will go off. Now you are driving around normally and it won't come back on until it gets hot sitting in traffic again

 

gingerbreadman1977 your thoughts are correct if you mount the switch on the "hot" side of the coolant.


That fan switch will work perfectly if you put it at the radiator outlet or even at the water pump inlet assuming the cooling system is up to par.

Your rad outlet temps should be somewhere around 20° or more less than you tstat temp, so if you are normally running 185°, the fans will stay off, but when stopped and the air flow thru the rad stops, the coolant radiator outlet temp will rise, the fans go on and the coolant will release heat again and lower the coolant temp to enter the engine and remove heat from the engine again.

 

So, the fans are blowing vigorously through a radiator that isn't flowing anything because the thermostat is closed...???

 

If he runs normally at 180-185°, then I assume he has a 180 tstat.
He said
So I would also assume the fans (turned on by the very hot coolant at the radiator outlet) would be blowing vigorously thru a radiator that is flowing lots of very hot coolant since the tstat is wide open (coolant at 195° sitting at lights).
Then after the coolant gets approximately 20° cooler than the tstat temp again (which should be 180-20=160) the fans will have shut off at 175° and if the situation arises where the coolant reaches 195° again, then they will turn on again and the cycle repeats.

The only way you can improve the temp control would be to put the tstat (lower temp of course) at the radiator outlet to control temp going into the engine. (which GM did in later years)

 

i have a 185 thermostat and want to keep it that way. radiator is awesome as well is fan but yes your right the thermostat wont permit me to go a lower temp except in winter when not even it can keep the temp up. i want to keep the 185 stat in there as thats the temp i like.

i think a much better system would be a switch that runs of the tach, if the revs drop below for example 1000rpm the fans come on. dont know if there is anything out there but i think that would work for me.

 

OK, so back to the original post.... Your fans won't turn off because your thermostat will keep the coolant temp above 175F. Your solution would be to install a 160F stat and let the fans and their temp switch regulate your coolant temperature...instead of the stat.

 

yeah thanks 7t1 i think it might be the way to go.i can only try it and hopefully my fan and radiator has the potential to reach below 175 although im thinking thats a big ask.

 

It's really a pretty basic concept.

The tstat regulates your engine temperature.

The fans (or airflow or fan switch or whoever you want to call it) regulates the coolant temp entering the engine.

Use an IR gun or pyrometer on the rad outlet with the fans off and on and you will see how the coolant works.

The Pantera used method this 37 years ago, as did other exotics.

 

Simple, get a switch that turns on at 205 and off at 185.

 

I've been trying to follow this thread and it sounds as if you want a minimum temp of 185 and a maximum of 195 "and" you "dont" want the electric fan cycling on and off.
Your a perfect candidate for a GM #88961768,this clutch fan with a 7 blade will blow away the electric fan with no extra load on your charging system.

 

COOLING SYSTEMS
When the engine is just started, the thermostat will be closed, restricting coolant flow through the entire system. Upon reaching 180 to 185 degrees (gingerbreadman's '77) it will open and allow coolant flow until the cool water from the radiator reaches it, whereby the thermostat will close and the process will continue. This cycle will continue, with the time the thermostat is open and flowing dependant on the amount of heat the cooling system can shed. (In cold climates and winter the thermostat may restrict flow - be closed- much of the time'while the reverse may be true in warmer climates and summer).

With the above in mind, lets look at the function of the cooling system fan. The fan is intended to increase the amount of heat the radiator will shed by artifically increasing airflow through it. The fan consumes engine power to do this, either directly (mechanical fan) or indirectly (electrical fan powered by the engine turning the alternator to generate current). It is generally desireable to minimize the power consumed by the fan to maximize performance and to increase fuel economy. To achieve the cooling boost while minimizing the use of an electric fan, you want to use it only when needed. This requires atemperature control switch. If you locate this switch in the engine, upstream of the cooling system thermostat, this switch is reading the temp being maintained by that engine's thermostat - in this case 180-185 degrees. If is 195 on and 175 off, initially the fan will be off, BUT if the engine ever sees 195 during a run, the fan will come on and will not stop operating until the engine is stopped. The engine thermostat will prevent the switch from ever 'seeing' the 175 degree shut off point.

If you want to properly use this switch, mount it in the lower hose, where the coolest water in the system occures. If your engine begins to overheat, your engine temp will begin to rise (to approx 215 degrees assuming that the radiator will shed approximately 20 degrees of heat), the fan will activate and begin to assist in further bringing down the temp of the radiator discharge water until it reaches 175 degrees when it turns off.

 

Good explaination. I was beginning to feel like the Lone Ranger



That is usually the best system for these cars.